This invention relates to the removal of anions from alkaline silicate solutions using a cationic ion exchange resin. In particular, it relates to the removal of HMO.sub.2.sup.- anions from Na.sub.2 O--SiO.sub.2 or K.sub.2 O--SiO.sub.2 solutions by contacting the solutions with a cationic ion exchange resin, where M is manganese, zinc, copper, or nickel.
Sodium silicate solutions have many industrial applications, some of which require high purity. In the electronics industry, for example, sodium silicate solutions are used to make colloidal silica. To prevent short circuiting, the solutions are required to have a very low metal content.
Sodium silicate solutions can be made by melting soda ash (sodium carbonate) with sand (SiO.sub.2), by dissolving amorphous silica and sodium hydroxide in water, or by other techniques. The starting materials are mined or obtained from other sources and generally contain significant amounts of metals. Many of the metals can be removed by known techniques, but some metals, such as manganese and zinc, are difficult to remove to the ppb (parts per billion, by weight) level that is sometimes required.